Fractured bones often are treated using fixation devices, which reinforce the fractured bone and keep it aligned during healing. Fixation devices may take a variety of forms, including casts for external fixation and bone plates for internal fixation.
Bone plates probably are the most common internal fixation device and typically are formed as a rigid metal plate that is mounted on a fractured bone to span or bridge the fracture. Bone plates typically are held in place by screws or other fasteners attached to the bone on each side of the fracture through apertures in the bone plate.
Bone plates are considered the treatment of choice for many fractured bones, especially long bones, because they are compact, permitting an early return to motion. However, bone plates suffer from a number of shortcomings. In particular, bones reinforced by bone plates are subject to refracture near the ends of the bone plate. The rate of such refracture may be several percent, increasing medical costs and healing time and decreasing productivity.
Refractures associated with bone plates tend to occur through screw holes in the bone near the ends of the bone plate. In an attempt to reduce refracture, some clinicians attach bone plates less strongly at their ends, for example, by using unicortical screws. Unicortical screws penetrate through only half of the bone, so that the bone plate is held less securely, and the bone is not weakened by screw holes across its entire thickness. Unfortunately, the use of unicortical screws has provided mixed results, decreasing the rate of some kinds of refracture but increasing the rate of other kinds.
In another attempt to reduce refracture, some vendors have produced bone plates that are tapered toward their ends to reduce rigidity. Unfortunately, such tapering makes the bone plate narrower at its ends, creating focal points for stress transfer. Moreover, some tapered bone plates are designed to be attached to the bone by increased numbers of screws near the ends, weakening the bone plate and bone in the area prone to refracture.